This is a request for a scientist Development Award to support training in molecular biological and biochemical approaches for studying receptor.based mechanisms of drug addiction The prolonged administration of certain addictive drugs causes sequestration and/or down regulation of G protein-coupled receptors. These phenomena involve drug-induced internalization of receptors from the plasma membrane and their delivery to specific populations of intracellular vesicles. The mechanisms that mediate and control this receptor internalization are not known. While several classes of cellular proteins have been identified that associate with receptors and mediate specific events in signal transduction, studies of mutant receptors and cell lines indicate that none of these associations is required for drug-induced receptor internalization. Therefore other, as yet unidentified, mechanisms must mediate and control drug-regulated internalization. By focusing on adrenergic receptors as a physiologically important and experimentally advantageous model system, the proposed studies will provide training in biochemical and molecular biological approaches to (1) define receptor domains that determine specific steps in the internalization mechanism, (2) identify cellular proteins that associate with receptors and mediate these steps, and (3) purify and clone these additional proteins. This work will elucidate, in molecular detail, fundamental biological mechanisms relevant to drug addiction.